1. Field of the Invention
The present invention generally relates to an outer mirror assembly, such as a door mirror assembly and a fender mirror assembly, for a motor vehicle and, more particularly, to an outer mirror assembly wherein the vibration of the mirror holder that occurs against the mirror visor during driving is prevented or attenuated.
2. Prior Art
For the prevention of such a vibration there have been proposed various means, one of which, officially disclosed under Japanese first Utility Model Publication No. 37857/1985, comprises a first vibration-preventive member provided to a mirror holder and a second vibration-preventive member in a mirror visor, each member placed in slidable contact with each other, as shown in FIG. 6.
In said means illustrated in FIG. 6, a mirror 1 is provided, as well as a mirror holder 2 which holds the back of the mirror 1, and a mirror-positioning unit 4 which tilts the mirror upwardly and downwardly as well as laterally. This mirror-positioning unit 4 is fixedly housed in a space interiorly defined by the mirror visor which is not shown in the drawings.
The mirror holder 2 has a coupling means 2a at its center and a case 4b of the mirror-positioning unit 4 also has a coupling means 4a. The coupling means 2a fitted with the coupling means 4a in such a manner as to be movable in a upwardly and downwardly and laterally tilting movement.
The mirror-positioning unit 4 has at least one mirror-driving rod 5, one end of which is relatively movably connected to the mirror holder 2. This rod 5 is generally threaded. A motor and a motive power transmission mechanism therefor are provided in the case 4b of the mirror-positioning unit. The motive power transmission mechanism includes a nut member (not shown) which is fitted over the rod 5. By rotation of this nut, the rod 5 is moved in axial directions in such a manner as to move said mirror holder 2 and to change the attitude of the mirror 1.
Both the mirror holder 2 and case 4b have at least two vibration-preventive members 3 or 4d. The two vibration-preventive members 3 and 4d face each other and come into contact with each other at their respective slidable contact surfaces 3a and 4c. Therefore, if a vibration occurs in a motor vehicle during driving, the occurrence of the relative chattering vibration which the mirror 1 (the mirror visor) produces against the case 4b is, the mirror visor, is effectively prevented.
In these vibration-preventive members 3 and 4d, each of the respective slidable contact surfaces 3a and 4c forms an arc having as the center a point O around which the mirror holder 2 is moved for changing the attitude of the mirror 1.
However, problems are involved in the practices where arcs are formed as stated above. Once a chattering vibration starts, caused by, for example, resonance in the mirror holder assembly, friction loses its effect. Therefore, chattering vibrations cannot be effectively prevented.